Automatic leveling system for an impression roller in a printing press

ABSTRACT

A system for automatically maintaining a desired relation between the axes of a printing cylinder and an impression roller movable toward and away from the printing cylinder by sensing the relative positions of the ends of the impression roller, and adjusting the relative displacement of the impression roller ends to attain the desired axial relationship between the printing cylinder and the impression roller.

United States Patent Inventor Appl. NO. Filed Patented Assignee AUTOMATIC LEVELING SYSTEM FOR AN IMPRESSION ROLLER IN A PRINTING PRESS [56] References Cited UNITED STATES PATENTS 2,607,292 8/1952 Harless etal. 101/153 3,272,122 9/1966 Behringer 101 247 x Primary Examiner-Robert E. Pulfrey Assistant Examiner.l. Reed Fisher Attorney-Brumbaugh, Graves, Donohue & Raymond ABSTRACT: A system for automatically maintaining a desired relation between the axes of a printing cylinder and an l0 Chums 6 Drawing Figs impression roller movable toward and away from the printing US. Cl 101/247 cylinder by sensing the relative positions of the ends of the im- Int. Cl l i. B411 13/40 pression roller, and adjusting the relative displacement of the Field of Search 101/216, impression roller ends to attain the desired axial relationship 247, 153 between the printing cylinder and the impression roller.

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Patentea Aug. 24, 1971 3,601,046

4 Sheets-Sheet 2 IN VENTOR.

JOHN C. MOTTER A TORNEYS 5 00 R S .E Y E RT T E 0 N I M 4 I 1. T W I 9 W C T [N A O o J 7 w w I 6 n T T l h w w a. 0 C M F Y S S I B w u". 9 .m L

PRESSURE LIMIT SWITCH Patented Aug. 24, 1971 4 Sheets-Sheet 4 LIMIT SWITCH LIMIT SWITCH SAFETY LIMIT SWITCH FIG. 5.

AUTOMATIC LEVELING SYSTEM FOR AN IMPRESSION ROLLER IN A PRINTING PRESS This invention relates to improvements in printing presses, and more particularly to a novel leveling system for maintaining a parallel relation between the axes of the rotatable elements forming a printing couple.

The leveling system of the present invention is applicable to a conventional printing press, such as a rotogravure printing press, in which an impression roller is supported between a pair of movable supporting frames which are adjustable to carry the impression roller toward or away from a printing cylinder mounted for rotation on a fixed axis.

In a conventional rotogravure printing press, the paper web is fed between a rotating printing cylinder and a rotating impression roller in tangential relationship with the printing cylinder, and ink impressions are printed on the paper web by utilizing depressions in the printing cylinder while the impression roller provides the desired pressure between the paper web and the printing surfaces of the printing cylinder. The impression roller is mounted between a pair of movable supporting frames which are guided for movement in the side frames of the printing press, and these supporting frames carry the impression roller toward or away from the printing cylinder. In large presses, these supporting frames are driven by a motor through a clutch so that the supporting frames can be moved in unison or one of the supporting frames can be moved separately to orient the axis of the impression roller relative to the axis of the printing cylinder. In moving the impression roller toward the printing cylinder, spring forces are built up and act on the supporting frames as soon as the movement of the impression roller is resisted by the printing cylinder. Therefore, when the impression roller is in operative, tangential relationship with the printing cylinder, the pressure engagement between the impression roller and the printing surfaces of the printing cylinder is determined by these spring forces.

' In printing paper webs of full width, it is customary to use a full length impression roller. From time to time, it becomes necessary to convert the press to print on a narrower web of paper from less than the full length of the printing cylinder, and in such instances, a shorter impression roller is employed to avoid direct contact between the printing cylinder and the impressionroller beyond the edge of the paper web. When it has been necessary to use impression rollers of less than full length, the press operators have encountered difficulty in obtaining uniform pressure between the impression roller and the printing cylinder throughout the length of the bite between the cylinders because of the tendency of the impression roller to tilt while it is brought into the desired pressure engagement with the printing cylinder. More specifically, when the shorter impression roller is moved by power into operative position with respect to the printing cylinder and substantially equal spring forces are exerted at opposite ends of the impression roller through the supporting frames, there is less resistance to the spring pressure at the short end than at the full length end, causing the supporting frame at the short end to travel a greater distance than the supporting frame at the full length end before sufficient spring pressure is built up, thereby tilting the axis of the impression roller downwardly at the short end thereof. The tilted relation of the impression roller to the printing cylinder produces higher pressure, and therefore heavier impressions and excessive wear, between the impression roller and the printing cylinder at the short end and lighter pressure, and therefore lighter impressions, at the full length end.

In my US. Pat. No. 3,254,598, which issued June 7, 1966 and is entitled Leveling Indicator For a Printing Press, is disclosed an indicating device for forewaming the operator of a tilted condition of the impression roller and also for helping him to correct it.

The purpose of the leveling system of the present invention is to adjust automatically the relative displacement of the impression roller supporting frames so as to maintain the desired parallel relation between the axes of the impression roller and the printing cylinder. Toward this end, each supporting frame is displaced by the drive motor through a corresponding clutch. The energization of the two clutches is controlled by two limit switches which are mounted on a member connected through a drive transmission with one of the supporting frames. A limit switch operating member is disposed adjacent each limit switch and is connected through a drive transmission with the other of the supporting frames. If the axis of the impression roller should tilt from the desired parallel relation with the axis of the printing cylinder, the appropriate one of the limit switches will be operated to actuate the one of the clutches which decouples the leading supporting frame from the drive motor. The lagging supporting frame is then driven until the tilt is corrected, at which time that one clutch limit switch is released. A short impression roller may thus be driven into operative relation with the printing cylinder until the desired pressure is obtained therebetween, at which time the drive motor is deenergized automatically by a pressure limit switch, and uniform impressions will be obtained across the width of the printed web. When the impression roller is withdrawn from the printing cylinder, the electrical connections between the limit switches and the clutches are automatically reversed, and the clutches are automatically operated as necessary to maintain a parallel relation between the axes of the impression roller and the printing cylinder, thereby preventing skewing and possible jamming of the impression roller in the side frames of the printing press.

For a complete understanding of the present invention, reference can be made to the detailed description which follows, and to the accompanying drawings in which:

FIG. 1 is a front view of a printing press equipped with the leveling system of the present invention;

FIG. 2 is an enlarged side elevation of part of the printing press shown in FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2, looking in the direction of the arrows;

FIG. 3A is a sectional view taken along the line 3A3A of FIG. 3, looking in the direction of the arrows;

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3, looking in the direction of the arrows, and

FIG. 5 is a schematic diagram of exemplary electrical circuitry for controlling the operation of the printing press shown in FIG. 1-4.

In the drawings, the leveling system of the present invention is shown installed on a conventional rotogravure printing press. The printing press comprises a printing cylinder 1, an impression roller 2 (shown in FIG. 1 as shortened at the right end by a reduction in diameter so that only the left end thereof is in pressure engagement with the printing cylinder), and an impression backup cylinder 3 for the impression roller. The printing cylinder 1 is supported for rotation in bearings 4 and 5 mounted in the side frames 6 and 7 of the press. The impression roller and the backup cylinder are supported for rotation between vertically movable supporting frames 8 and 9. The left (as viewed in FIGS 1 and 3) supporting frame 8 is equipped with gibs 8a which guide it for vertical movement in the left side frame 6, and the right supporting frame 9 is equipped with gibs 9a which guide it for vertical movement in the right side frame 7.

Referring to FIG. 1, the supporting frames 8 and 9 are movable in their respective side frames to translate the impression roller and backup cylinder toward and away from the printing cylinder under the power of a motor 10 supported from a crossbeam 11 suspended between the side frames at the top of the press. A shaft 12, supported for rotation between the side frames of the press above the impression and backup rollers, is driven in either direction by the motor 10 through a gear transmission enclosed within a housing 13. One end of the shaft 12 transmits motion through a left clutch 14 to raise or lower the left supporting frame 8. The clutch 14 is normally disengaged by a spring 15, but may be engaged through a linkage 16 by a solenoid 17 mounted on the side frame 6. Similarly, the other end of the shaft 12 transmits motion through a right clutch 19 to raise or lower the right supporting frame 9. The clutch 19 is biased by a spring 20 so as to be normally disengaged, but may be engaged through a linkage 21 by a solenoid 22 mounted on the side frame 7. When both clutches l4 and 19 are engaged, the motor imparts motion to both supporting frames in unison. When one of the clutches is disengaged, the motor remains operatively connected to the opposite supporting frame. Accordingly, by disengaging the proper clutch, the supporting frames can be adjusted relative to each other to change the angle of the axis of rotation of the impression roller 2.

The means for translating the rotational movement of the shaft 12 into vertical movement of the supporting frames 8 and 9 is conventional and need not be described herein in detail. For present purposes it suffices to say that each of the supporting frames 8 and 9 is supported from the lower end of a vertically disposed screw 25. Each of the screws extends upwardly from the respective supporting frame and passes through a gear housing 26, and the upper end of the screw is accommodated within a housing 27 containing a spring. The gear housing 26 contains a gear system through which upward and downward motion is imparted to the screws depending on the direction of rotation of the shaft 12. When the screws 25 are moving downwardly to carry the impression roller into operative position with the printing cylinder and the further downward movement of the impression roller is resisted by the printing cylinder, the springs within the housings 27 begin to build up spring forces which increase to predetermined values before the motor 10 is automatically cut off by a conventional pressure limit switch 29 which is mechanically coupled to the spring within the housing 27 mounted on the left side frame 6. For convenience, the pressure limit switch 29 includes an indicator to show the load on the left supporting frame 8. The spring forces are transmitted to opposite ends of the impression roller through the screws 25 and the respective supporting frames.

When a full length roller is carried between the supporting frames 8 and 9, the substantially equal spring forces which are transmitted to opposite ends of the impression roller through the supporting frames 8 and 9 produce a relatively uniform impression along the entire length of the bite between the printing cylinder and impression roller. However, as explained above, when an impression roller short at one end is substituted for the full length impression roller, the axis of the impression roller may tend to' tilt by reason of the overtravel of the supporting frame 9 at the short end of the impression roller, causing excessive wear and heavy impressions on the right end (as viewed in FIG. I) of the paper web passing between the printing cylinder and the impression roller and lighter impressions at the full length end at the left.

In order to adjust automatically the relative displacement of the impression roller supporting frames 8 and 9 so as to maintain the desired parallel relation between the axes of the impression roller 2 and the printing cylinder 1, the printing press according to the present invention is provided with a pair of limit switches 31 and 32, which may be operated by means to be described below to disengage the appropriate one of the clutches l4 and 19, as necessary. The limit switches 31 and 32 are mounted on a plate 34, which is secured by a plurality of screws 35 to the left end (see FIG. 3) of a hollow shaft 37, which in turn is mounted for rotation within the left side frame 6. The end of the outer shaft 37 remote from the plate 34 extends beyond the inner surface of the side frame 6 and forms a pinion 39, which meshes with a vertically movable rack 40 secured to the left supporting frame 8 by a plurality of screws 42. Accordingly, vertical movement of the supporting frame 8 imparts rotation to the plate 34.

An inner shaft is mounted for rotation within the outer shaft 37, and the right end of the inner shaft extends beyond the corresponding end of the outer shaft and is received for rotation within the right side frame 7. A pinion 46 is affixed to the end of the inner shaft 45 adjacent the inner face of the side frame 7, and the pinion meshes with a vertically movable rack 48 secured to the right supporting frame 9 by a plurality of screws 50.

A gear 52 is affixed to the opposite end of the inner shaft 45, which end extends beyond the plate 34. Accordingly, vertical movement of the supporting frame 9 imparts rotation to the gear 52. The gear 52 meshes with a pinion 54 mounted for rotation on a shaft 55, which is secured to the plate 34. Secured to the pinion 54 for rotation therewith is a plate 56 which carries a pair of studs 57 and 58 adapted to engage the arms 31a and 32a of the limit switches 31 and 32, respectively. The studs 57 and 58 are eccentrically mounted on the plate 56 to enable the operation of the limit switches to be adjusted precisely, and the studs may be locked in the desired positions by a pair of setscrews 59 and 60, respectively.

If the axes of the impression roller 2 and the printing cylinder 1 are parallel while the impression roller is being driven toward or away from the printing cylinder, the shafts 37 and 45 will be driven at the same angular speed, inasmuch as the gear ratios between the racks 40 and 48, and the corresponding pinions 39 and 46, respectively, will be identical. In this situation, the angular speeds of the gear 52 and the plate 34 will be identical, and the plate 56 will be static with respect to the plate 34 and will be in the neutral position illustrated in FIG. 3A.

When the impression roller 2 is brought into engagement with the printing cylinder 1 and begins to tilt due to the overtravel of the right supporting frame 9, the right rack 48 will travel farther than the left rack 40, causing the inner shaft 45 to rotate clockwise through a greater angular distance than does the outer shaft 37. Accordingly, the gear 52 will rotate clockwise (as viewed in FIG. 3A) through a greater angular distance than will the plate 34 and the shaft 55 secured thereto. Thus, the pinion 54 and the plate 56 secured thereto will be rotated counterclockwise about the shaft .55 by the gear 52, and the limit switch 31 will be operated by the stud 57 to disconnect the right supporting frame 9 from the drive motor 10. Similarly, if the impression roller were foreshortened at the left end so that it tilted by reason of the overtravel of the left supporting frame 8, the plate 34 would be rotated clockwise through a greater angular distance than the gear 52, so that the plate 56 would be rotated about the shaft 55 in the clockwise direction, causing the stud 58 to operate the limit switch 32 and disconnect the left supporting frame 8 from the drive motor 10.

A safety limit switch 63 mounted on the plate 34 prevents the leveling system from going out of adjustment and prevents any of the elements of the printing press from being damaged, in the event that either of the clutches 14 and 19 should malfunction and thereby fail to disconnect one of the supporting frames 8 and 9 from the drive motor 10. The arm 63a of the limit switch 63 is engaged by one of a pair of studs 65 and 66 when the relative displacement between the gear 52 and the plate 34 isgreater than that which is required to normally operate the limit switches 31 and 32, respectively. The studs 65 and 66 are mounted on collars 67 and 68, respectively, which in turn may be locked at the desired angular positions with respect to the inner shaft 45 by means of setscrews 69 and 70, respectively.

The electrical connections to the two limit switches 31 and 32 and to the safety limit switch 63 are made through four slip rings 74 mounted on the outer shaft 37, one of the slip rings being a common connection to one terminal of each of the switches. The electrical connections to the sliprings 74 are made by four brushes 75 which are mounted on the inside of a housing 77 which encloses the gear 52, the plate 34 and the components mounted thereon. The housing 77 is secured to the left side frame 6 by a plurality of screws 78, and an inspection plate 80 may be readily removed for adjustment or replacement of any of the elements within the housing.

The operation of the leveling system will now be described in conjunction with the electrical control circuitry illustrated in FIG. 5. The circuit components are connected between a power conductor 85, which may be connected to a suitable source 86 of electric power by a switch 87, and a ground return conductor 88.

In order to drive the impression roller 2 toward the printing cylinder 1, the Down" switch 90 is closed thereby energizing a relay solenoid 91. The relay 91 remains energized through the holding contact 91a, regardless of the condition of the switch 90, until the normally closed pressure limit switch 29a is opened. The normally closed contact 91b is opened, thereby disarming the relay solenoid 92, which is energized when the impression roller is to be withdrawn from the printing cylinder.

The normally open contact 91c of the relay 91 is closed, energizing the armature and field windings 93 and 94 of the drive motor 10, and the impression roller is driven downwardly toward the printing cylinder until the springs within the housings 27 develop the predetermined spring forces at which the pressure limit switch 29 is automatically opened to deenergize the drive motor 10.

If the right supporting frame 9 begins to advance with respect to the left supporting frame 8, due to the impression roller being tilted after it engages the printing cylinder or for any other reason, the gear 52 will be rotated clockwise to a greater angular extent than the plate 34, and so the plate 56 will be rotated counterclockwise until the stud 57 closes the limit switch 31, thereby energizing a relay solenoid 96, inasmuch as the normally open contact 91d is closed when the relay 91 is energized by the Down switch 90.

The normally closed contact 96a of the relay 96 is opened, thereby deenergizing the right solenoid 22. The right clutch 19 is disengaged by the biasing spring 20, decoupling the right supporting frame 9 from the drive motor 10. The drive motor continues to drive the left supporting frame 8 until the left supporting frame reaches the desired relative position with respect to the right supporting frame, at which time the axes of the impression roller and the printing cylinder will be parallel. As this condition is reached, the plate 56 is rotated clockwise around the shaft 55, opening the limit switch 31 and energizing the right solenoid 22, which in turn overcomes the force of the biasing spring 20 to engage the clutch 19. The drive motor 10 then drives both of the supporting frames 8 and 9 in unison until the predetermined spring forces build up in the springs inside the housings 27, or until the impression roller is again tilted for some reason.

if an impression roller is used which is short at the left end, or if for any reason the impression roller 2 is tilted so that the left supporting frame 8 advances or overtravels with respect to the right supporting frame, the plate 34 will be rotated in the clockwise direction with respect to the gear 52, resulting in a clockwise rotation of the plate 56 until the stud 58 operates the limit switch 32. The closing of the limit switch 32 energizes a relay solenoid 97, inasmuch as the normally open contact 9le is closed when the relay 91 is energized by the Down" switch 90. The normally closed contact 97a is opened, thereby deenergizing the left solenoid l7, whereupon the biasing spring disengages the left clutch 14 to decouple the left supporting frame 8 from the drive motor. The drive motor continues to drive the right supporting frame 9 until the ,desired parallel relationship is attained between the axes of the impression roller and the printing cylinder. As this condition is reached, the plate 56 is rotated counterclockwise, opening the limit switch 32. The left solenoid 17 is energized, engaging the clutch l4, and both of the supporting frames are again driven in unison.

The impression roller is thus driven into operative relation with the printing cylinder until the desired pressure is obtained therebetween at which time the drive motor is deenergized automatically by the pressure limit switch 29a. In particular, the normally closed switch 29a is opened, deenergizing the relay solenoid 91 and opening the contact 91c thereof. The automatic leveling system according to the present invention'insures that the desired parallel relationship exists between the axes of the impression roller and the printing cylinder, so that uniform impressions will be obtained across the width of the printed web. I

When the pressure limit switch 29 is operated to open the normally closed switch 29a, the normally open pressure limit switch 29b is simultaneously closed to energize the drive motor reversing relay 102, which remains energized through the holding contact 102a, regardless of the condition of the limit switch 29b. The normally closed contacts 102b and 102C are opened and the normally open contacts 102d and 102e are closed to reverse the connection of the field coil 94 in the circuit, so that the drive motor 10, when again energized by closing the Up switch 100, will rotate in the opposite direction and withdraw the impression roller from the printing cylinder.

When it is desired to withdraw the impression roller from the printing cylinder, the Up" switch is closed to energize the relay solenoid 92, this relay remaining energized through the holding contact 92a, regardless of the condition of the switch 100, until a normally closed Pull Up limit switch 101a is opened. The Pull Up limit switch (not shown) may be mounted on one of the side frames and is engaged by the corresponding one of the supporting frames when the impression roller has been fully withdrawn from the printing cylinder. The normally closed contact 92b is opened, thereby disarming the solenoid 91, which is energized when the impression roller is lowered.

The nonnally open contact 920 of the relay 92 is also closed, energizing the armature and field windings 93 and 94 of the drive motor to withdraw the impression roller from the printing cylinder. When the impression roller has been withdrawn to the Full Up position and the normally closed limit switch 101a is opened to deenergize the drive motor, a normally closed Full Up limit switch 101b is also opened, deenergizing the drive motor reversing relay 102, so that when the drive motor is again energized it will drive the impression roller toward the printing cylinder.

If the impression roller should become tilted for some reason while being withdrawn from the printing cylinder, the plate 56 will be rotated in the appropriate direction to operate one of the limit switches 31 and 32 to decouple the proper one of the supporting frames 8 and 9 from the drive motor and thereby correct the tilted condition. In order that the drive motor be disconnected from the advancing or leading one of the supporting frames, the electrical connections between the limit switches 31 and 32 and the relay solenoids 96 and 97 must be reversed, since the leading supporting frame when the impression roller is being raised will be the uppermost supporting frame, while the leading supporting frame when the impression roller is being lowered will be the lowermost supporting frame. Accordingly, when the relay solenoid 92 is energized by closing the Up switch 100, the limit switch 31 is connected to the relay solenoid 97 by the contact 92d, and the limit switch 32 is connected to the relay solenoids 96 by the contact 92c.

If one of the clutches l4 and 19 should malfunction so that the relative rotational displacement between the gear 52 and the plate 34 exceeds that which should operate one of the limit switches 31 and 32, one of the studs 65 and 66 will close the safety limit switch 63, thereby energizing a relay solenoid 104 to open the normally closed contacts 104a and 104b. This deenergizes the relay solenoids 91 and 92, opening the contacts 91c and 92c and deenergizing the drive motor 10, no matter which direction it is rotating. A normally closed override switch 105 is provided so that the safety limit switch 63 may be neutralized for trouble shooting, adjustment, or the like. A normally closed safety switch 107 is also provided so that the drive motor 10 may be deenergized at anytime.

The invention has been shown in a single preferred embodiment and by way of example only, and obviously many modifications and variations can be made therein without departing from the spirit of the invention. For example, although the means disclosed for displacing the impression roller and applying impression pressure is an electric motor, it is apparent that the automatic leveling system according to the present invention is readily applicable to a hydraulic or pneumatic system, the limit switches operating suitable valves, for example. The invention, therefore, is not to be limited to any particular form or embodiment except insofar as such limitations are expressly set forth in the appended claims.

I claim:

1. In a printing press which includes a pair of side frames, a printing cylinder supported between the side frames for rotation, an impression roller movable toward and away from the printing cylinder, a pair of movable supporting frames guided for movement within the side frames and carrying the impression roller therebetween, drive means for imparting movement to the supporting frames in unison or for imparting movement to one of the supporting frames relative to the other, and means formoving the supporting frames toward and away from the printing cylinder and applying a spring force on each of the supporting frames after the impression roller is brought into pressure engagement with the printing cylinder, means for maintaining a desired relationship between the axes of the impression roller and the printing cylinder comprising means mounted on at least one of the side frames and coupled to the supporting frames for sensing the relative positions of the supporting frames, and means responsive to the sensing means and coupled to the drive means for controlling the drive means to displace one of the supporting frames to the desired position with respect to the other supporting frame.

2. The relationship maintaining means according to claim 1 wherein the sensing means includes switch means mounted on one of the side frames and coupled to one of the supporting frames for movement therewith, and a switch means activating member mounted on one of the side frames and disposed in operative relationship with the switch means and coupled to the other supporting frame for movement therewith, and wherein the drive controlling means includes means for selectively coupling the drive means with at least one of the supporting frames.

3. The relationship maintaining means according to claim 2 wherein -the selective coupling means includes a clutch, and the drive controlling means includes an electromechanical transducer connected to the clutch and controlled by the switch means.

4, The relationship maintaining means according to claim 2 including a pair of shafts, one imparting movement to the switch means and the other imparting movement to the switch means-activating member, one end of the one shaft in driving relationship to the switch means and one end of the other shaft in driving relationship to the switch means-activating member, a drive transmission connecting the one shaft with the one supporting frame, and a drive transmission connecting the other shaft with the other supporting frame.

5. The relationship-maintaining means according to claim 4 wherein the pair of shafts are concentric, and each transmission includes a pinion carried by the respective shaft and a rack carried by the respective supporting frame and in driving relation with the pinion.

6. A printing press comprising a pair of side frames, a printing cylinder supported between the side frames for rotation, an impression roller, a pair of supporting frames guided for movement within the side frames and supporting the impression roller therebetween, drive means for imparting movement to the supporting frames in unison or for imparting movement to one of the supporting frames relative to the other, means for moving the supporting frames toward and away from the printing cylinder and applying a spring force on each of the supporting frames after the impression roller is brought into pressure engagement with the printing cylinder, switch means mounted on one of the side frames and coupled to one of the supporting frames for movement therewith,

means mounted on one of the side frames for activating the switch means, the activating means being disposed in operative relationship with the switch means and coupled to the other supporting frame for movement therewith, and means responsive to the switch means for selectively coupling the drive means with at least one of the supporting frames.

7. A printing press according to claim 6 wherein the switch means includes a pair of switches, one of the switches disposed so as to be activated by the activating means when a first relationship exists between the axes of the impression roller and the printing cylinder, the other switch disposed so as to be activated by the activating means when a second relationship exists between the axes of the impression roller and the printing cylinder, and the selective coupling means includes a pair of clutches, each clutch coupling the drive means with a different one of the supporting frames, each clutch being controlled by a different one of the switches.

8. A printing press according to claim 6 including a pair of coaxial shafts, one in driving relationship and imparting movement to the switch means and the other in driving relationship and imparting movement to the switch activating means, a drive transmission connecting one shaft with one of the supporting frames, and a drive transmission connecting the other shaft with the other supporting frame.

9. A printing press according to claim 6 wherein the switch means and the switch-activating means are adjacent one of the side frames, and including a pair of concentric rotatable shafts, one shaft carrying the switch means and the other shaft carrying the switch-activating means, a drive transmission connecting the outer shaft with the one supporting frame guided for movement in the side frame nearest the switch means and the switch-activating means, the inner shaft extending to the opposite side frame, and a drive transmission connecting the inner shaft with the other supporting frame guided for movement in the side frame furthest away from the switch means and the switch-activating means.

10. A printing press according to claim 9 wherein each drive transmission includes a pinion carried by the respective shaft and a rack carried by the respective supporting frame and in driving relation with the pinion. 

1. In a printing press which includes a pair of side frames, a printing cylinder supported between the side frames for rotation, an impression roller movable toward and away from the printing cylinder, a pair of movable supporting frames guided for movement within the side frames and carrying the impression roller therebetween, drive means for imparting movement to the supporting frames in unison or for imparting movement to one of the supporting frames relative to the other, and means for moving the supporting frames toward and away from the printing cylinder and applying a spring force on each of the supporting frames after the impression roller is brought into pressure engagement with the printing cylinder, means for maintaining a desired relationship between the axes of the impression roller and the printing cylindEr comprising means mounted on at least one of the side frames and coupled to the supporting frames for sensing the relative positions of the supporting frames, and means responsive to the sensing means and coupled to the drive means for controlling the drive means to displace one of the supporting frames to the desired position with respect to the other supporting frame.
 2. The relationship maintaining means according to claim 1 wherein the sensing means includes switch means mounted on one of the side frames and coupled to one of the supporting frames for movement therewith, and a switch means activating member mounted on one of the side frames and disposed in operative relationship with the switch means and coupled to the other supporting frame for movement therewith, and wherein the drive controlling means includes means for selectively coupling the drive means with at least one of the supporting frames.
 3. The relationship maintaining means according to claim 2 wherein the selective coupling means includes a clutch, and the drive controlling means includes an electromechanical transducer connected to the clutch and controlled by the switch means. 4, The relationship maintaining means according to claim 2 including a pair of shafts, one imparting movement to the switch means and the other imparting movement to the switch means-activating member, one end of the one shaft in driving relationship to the switch means and one end of the other shaft in driving relationship to the switch means-activating member, a drive transmission connecting the one shaft with the one supporting frame, and a drive transmission connecting the other shaft with the other supporting frame.
 5. The relationship-maintaining means according to claim 4 wherein the pair of shafts are concentric, and each transmission includes a pinion carried by the respective shaft and a rack carried by the respective supporting frame and in driving relation with the pinion.
 6. A printing press comprising a pair of side frames, a printing cylinder supported between the side frames for rotation, an impression roller, a pair of supporting frames guided for movement within the side frames and supporting the impression roller therebetween, drive means for imparting movement to the supporting frames in unison or for imparting movement to one of the supporting frames relative to the other, means for moving the supporting frames toward and away from the printing cylinder and applying a spring force on each of the supporting frames after the impression roller is brought into pressure engagement with the printing cylinder, switch means mounted on one of the side frames and coupled to one of the supporting frames for movement therewith, means mounted on one of the side frames for activating the switch means, the activating means being disposed in operative relationship with the switch means and coupled to the other supporting frame for movement therewith, and means responsive to the switch means for selectively coupling the drive means with at least one of the supporting frames.
 7. A printing press according to claim 6 wherein the switch means includes a pair of switches, one of the switches disposed so as to be activated by the activating means when a first relationship exists between the axes of the impression roller and the printing cylinder, the other switch disposed so as to be activated by the activating means when a second relationship exists between the axes of the impression roller and the printing cylinder, and the selective coupling means includes a pair of clutches, each clutch coupling the drive means with a different one of the supporting frames, each clutch being controlled by a different one of the switches.
 8. A printing press according to claim 6 including a pair of coaxial shafts, one in driving relationship and imparting movement to the switch means and the other in driving relationship and imparting movement to the switch activating means, a drive transmission connecting one shafT with one of the supporting frames, and a drive transmission connecting the other shaft with the other supporting frame.
 9. A printing press according to claim 6 wherein the switch means and the switch-activating means are adjacent one of the side frames, and including a pair of concentric rotatable shafts, one shaft carrying the switch means and the other shaft carrying the switch-activating means, a drive transmission connecting the outer shaft with the one supporting frame guided for movement in the side frame nearest the switch means and the switch-activating means, the inner shaft extending to the opposite side frame, and a drive transmission connecting the inner shaft with the other supporting frame guided for movement in the side frame furthest away from the switch means and the switch-activating means.
 10. A printing press according to claim 9 wherein each drive transmission includes a pinion carried by the respective shaft and a rack carried by the respective supporting frame and in driving relation with the pinion. 